1. Field
This disclosure relates to a thin film semiconductor device and a method for manufacturing the thin film semiconductor device.
2. Description of the Related Art
Thin film transistors (TFTs) are widely used as switching devices or driving elements of active-matrix display devices such as liquid crystal display devices and organic electroluminescence (EL) display devices.
In recent years, TFTs that include channel layers composed of oxide semiconductors such as zinc oxide (ZnO), indium gallium oxide (InGaO), and indium gallium zinc oxide (InGaZnO) have been actively researched and developed. TFTs that contain oxide semiconductors in channel layers feature low OFF current and high carrier mobility even in an amorphous state and can be manufactured through low-temperature processes.
Japanese Unexamined Patent Application Publication No. 2007-311404 discloses a technique for producing TFTs having stable characteristics. According to this technique, a heat treatment is performed after formation of an oxide semiconductor film. International Publication No. 2012/090490 discloses a technique of performing a plasma treatment such as an ozone treatment on an oxide semiconductor film after formation of the oxide semiconductor film and before formation a protective film. It also discloses that this plasma treatment suppresses occurrence of oxygen defects in the oxide semiconductor film.
In forming thin film semiconductor devices by the techniques described above, a plasma treatment is performed on an oxide semiconductor film to suppress occurrence of oxygen defects; however, the conditions of the plasma treatment are not disclosed. Thus, the oxide semiconductor may be damaged by the plasma treatment and the characteristics may become degraded depending on the conditions.